Misconceptions and Confusions in U-Pb dating

Submitted as coursework for Physics , Stanford University, Winter Introduction The majority of ionizing radiation around us and in us comes from natural sources: Like stable elements, radioactive isotopes help define the structure of materials and the way in which they interact with their environment. We can use their physical signatures, like half lives and relative concentrations, to determine the age and origin of composite materials — minerals, animal bones, planets, etc.. A primordial isotope is one that has existed in it’s present state on Earth for the lifetime of the earth. Of these, the decay processes of Uranium and Thorium contribute the most to the background radiation spectrum by a substantial margin. Potassium has the highest concentrations because it is ubiquitous in biological materials, while Uranium and Thorium are found primarily in rocks and soil particularly igneous rocks like granite [3]. In fact, most of the radiation to which we are exposed comes from the accumulated Potassium in our bodies and concentrations of these three isotopes in the soil. Langham conducted an experiment that showed that the amount of potassium in the body spiked around age 10 for women and age 20 for men.

Uranium-lead dating – The Full Wiki

Decay routes[ edit ] The above uranium to lead decay routes occur via a series of alpha and beta decays, in which U with daughter nuclides undergo total eight alpha and six beta decays whereas U with daughters only experience seven alpha and four beta decays. The term U—Pb dating normally implies the coupled use of both decay schemes in the ‘concordia diagram’ see below.

However, use of a single decay scheme usually U to Pb leads to the U—Pb isochron dating method, analogous to the rubidium—strontium dating method. Finally, ages can also be determined from the U—Pb system by analysis of Pb isotope ratios alone. This is termed the lead—lead dating method.

Uranium lead dating calculator Wired offers an important radioactive dating is u. Together with a radioactive isotope is the some practical examples of rocks and more.

U-Pb dating uses the relative presence of parent isotopes of uranium U and U and their daughter species of lead Pb and Pb respectively to determine the age of crystallisation of certain minerals. Together they provide two separate decay schemes to determine ages of crystallisation of minerals ranging from about 10 million years, up to and beyond the age of the earth at 4.

Zircon is a particularly valuable mineral for this purpose for the following reasons: It incorporates uranium but little lead during crystallisation and therefore a high proportion of radiogenic lead ie lead which has arisen by the radioactive decay of uranium in zircon has resulted from the in situ decay of uranium It is extremely resistant to chemical weathering or leaching. Once crystallised, it is very difficult to add or remove lead or uranium — it is a closed system It is extremely resistant to physical weathering — it is hard and crystals can survive for a long time.

Under extreme conditions, such as those that pertain in a major bolide event, a quantity of the lead is removed from the crystal matrix, thus partially or totally resetting the crystal. A set of such shocked crystals provides data that allows the date of original crystallisation and the date of resetting to be determined.

Earlham College – Geology – Radiometric Dating

While there are numerous natural processes that can serve as clocks, there are also many natural processes that can reset or scramble these time-dependent processes and introduce uncertainties. To try to set a reasonable bound on the age, we could presume that the Earth formed at the same time as the rest of the solar system. If the small masses that become meteorites are part of that system, then a measurement of the solidification time of those meteorites gives an estimate of the age of the Earth.

The following illustration points to a scenario for developing such an age estimate. Some of the progress in finding very old samples of rock on the Earth are summarized in the following comments. It is a compound of zirconium, silicon and oxygen which in its colorless form is used to make brilliant gems.

Uranium, on the other hand, is so well studied that its decay constant is much better known, making the U/Pb dating technique more accurate, Mundil noted. U/Pb dating relies upon the decay of naturally occurring uranium and different isotopes of lead.

A Abbreviations This information is included in Appendix A: Abbreviations , which includes all abbreviations and acronyms used in the Factbook, with their expansions. Acronyms An acronym is an abbreviation coined from the initial letter of each successive word in a term or phrase. In general, an acronym made up of more than the first letter of the major words in the expanded form is rendered with only an initial capital letter Comsat from Communications Satellite Corporation; an exception would be NAM from Nonaligned Movement.

Administrative divisions This entry generally gives the numbers, designatory terms, and first-order administrative divisions as approved by the US Board on Geographic Names BGN. Changes that have been reported but not yet acted on by the BGN are noted.

Changing Views of the History of the Earth

Radiometric Dating Radiometric Dating – A Brief Explanation Radiometric dating is the primary dating scheme employed by scientists to determine the age of the earth. Radiometric dating techniques take advantage of the natural decay of radioisotopes. An isotope is one of two or more atoms which have the same number of protons in their nuclei, but a different number of neutrons. Radioisotopes are unstable isotopes:

The generally accepted age for the Earth and the rest of the solar system is about billion years (plus or minus about 1%). This value is derived from several.

For example Uranium to lead, or carbon 14 to carbon 12 carbon dating. These methods rely on 3 assumptions: Hard to be sure when the half life can be millions of years, and there is some evidence that the decay rate has not been constant. Quite a big assumption if the rock is meant to have been sitting there for millions of years! Easy to understand article here, which clearly explains how radiometric dating works. Note that it is clearly suspect.

Rock from Mt St Helens volcano was dated as millions of years old when it is known to be just decades.

Dating | geochronology | localhost:81

Zircon incorporates uranium and thorium atoms into its crystalline structure, but strongly rejects lead. Therefore we can assume that the entire lead content of the zircon is radiogenic. Where this is not the case, a correction must be applied. These minerals often produce lower precision ages than igneous and metamorphic minerals traditionally used for age dating, but are more common in the geologic record. Interaction between mineralogy and radioactive breakdown During the alpha decay steps, the zircon crystal experiences radiation damage, associated with each alpha decay.

Uranium-lead dating is a radiometric dating method that uses localhost:81 can disturb the zircon and release the lead created from the localhost:81 had been so very cheap, and blood uranium lead dating zircon had flowed so freely, that the public ear had dulled .

The Radiometric Dating Game Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium. On the surface, radiometric dating methods appear to give powerful support to the statement that life has existed on the earth for hundreds of millions, even billions, of years. We are told that these methods are accurate to a few percent, and that there are many different methods.

We are told that of all the radiometric dates that are measured, only a few percent are anomalous. This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points. Since there doesn’t seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.

However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old. If these dates are correct, this calls the Biblical account of a recent creation of life into question.

After study and discussion of this question, I now believe that the claimed accuracy of radiometric dating methods is a result of a great misunderstanding of the data, and that the various methods hardly ever agree with each other, and often do not agree with the assumed ages of the rocks in which they are found. I believe that there is a great need for this information to be made known, so I am making this article available in the hopes that it will enlighten others who are considering these questions.

Even the creationist accounts that I have read do not adequately treat these issues.

Radiometric dating – Wikipedia

General considerations Distinctions between relative-age and absolute-age measurements Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled. This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.

For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built. Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence. Although with clever detective work many complex time sequences or relative ages can be deduced, the ability to show that objects at two separated sites were formed at the same time requires additional information.

A coin, vessel, or other common artifact could link two archaeological sites, but the possibility of recycling would have to be considered.

In dating: Fission-track dating during the spontaneous fission of uranium In this unique type of radioactive decay, the nucleus of a single parent uranium atom splits into two fragments of similar mass with such force that a trail of crystal damage is left in the mineral.

As evident by the equation, initial Pb isotope ratios, as well as the age of the system are the two factors which determine the present day Pb isotope compositions. This was first established by Nier et al. The Pb ratios of three stony and two iron meteorites were measured. By dating meteorites Patterson was directly dating the age of various planetesimals. As planetesimals collided, various fragments were scattered and produced meteorites.

Iron meteorites were identified as pieces of the core, while stony meteorites were segments of the mantle and crustal units of these various planetesimals. Iron meteorite found in Canyon Diablo Meteorite impact Figure 1. Pb—Pb isochron diagram Samples of iron meteorite from Canyon Diablo Meteor Crater Arizona were found to have the least radiogenic composition of any material in the solar system. Therefore, troilite found in Canyon Diablo represents the primeval lead isotope composition of the solar system, dating back to 4.

Together, these samples define an isochron, whose slope gives the age of meteorites as 4.

Radiometric Dating

Uranium glass glowing under UV light Before and, occasionally, after the discovery of radioactivity, uranium was primarily used in small amounts for yellow glass and pottery glazes, such as uranium glass and in Fiestaware. This waste product was diverted to the glazing industry, making uranium glazes very inexpensive and abundant. Besides the pottery glazes, uranium tile glazes accounted for the bulk of the use, including common bathroom and kitchen tiles which can be produced in green, yellow, mauve , black, blue, red and other colors.

Uranium glass used as lead-in seals in a vacuum capacitor Uranium was also used in photographic chemicals especially uranium nitrate as a toner , [9] in lamp filaments for stage lighting bulbs, [23] to improve the appearance of dentures , [24] and in the leather and wood industries for stains and dyes. Uranium salts are mordants of silk or wool.

Uranium-Lead Dating Uranium-lead dating is one of the most complicated of all dating techniques. This is in part because uranium and lead are not retained in rocks as easily as some others, and in part because the parent isotopes and daughter products are not even directly related.

Science Advisor Drakkith said: I think these will act mostly as sources of errors, unless accounted for. For example, if you only count lead and uranium, and ignore all the intermediaries, then you’ll end up underestimating the initial uranium content and the age estimate will be too high. The details of the dating process are less clean-and-easy than the outline provided earlier would suggest.

For one, there are two primordial isotopes of uranium, each with its own decay chain leading to different isotopes of lead. Another omission is that zirconium can also accommodate thorium in its lattice at formation but its half life is measured in hours or days, depending on the parent isotope, so it’s one of those intermediaries that you can ignore. Yet another issue is isolating homogeneous samples and not e.

I’m sure davenn can give you more nitty-gritty details, since he seems to have had some hands-on experience. In isolation it only gives you the lower bound for the age of the planet, or more specifically for the earliest time its surface cooled down sufficiently for crystals of this particular mineral to grow.

Uranium | chemical isotope | localhost:81

The four isotopes are uranium , uranium , lead , and lead The process of dating finds the two ratios between uranium and lead ; and uranium and lead The radiometric dater then uses the half-life of all four isotopes to find an age range the rock should be in. The half-lives of the cascade from uranium to lead has been been extrapolated to about million years and the cascade form uranium to lead has been calculated to about 4. This data is compared to a curve called the Concordia diagram.

This diagram has been made by using the ratio of uranium to lead of all the rocks dated with this method and their assumed age.

of lead or present in a sample. How does it work? Isoptopes often have unstable nuclei and undergoes decay to stable element. Uranium and are.

Both isotopes are the starting points for complex decay series that eventually produce stable isotopes of lead. Uranium—lead dating was applied initially to uranium minerals, e. The amount of radiogenic lead from all these methods must be distinguished from naturally occurring lead, and this is calculated by using the ratio with Pb, which is a stable isotope of the element then, after correcting for original lead, if the mineral has remained in a closed system, the U: If this is the case, they are concordant and the age determined is most probably the actual age of the specimen.

These ratios can be plotted to produce a curve, the Concordia curve see concordia diagram. If the ages determined using these two methods do not agree, then they do not fall on this curve and are therefore discordant. This commonly occurs if the system has been heated or otherwise disturbed, causing a loss of some of the lead daughter atoms. Because Pb and Pb are chemically identical, they are usually lost in the same proportions.

The plot of the ratios will then produce a straight line below the Concordia curve. Wetherill has shown that the two points on the Concordia curve intersected by this straight line will represent the time of initial crystallization and the time of the subsequent lead loss. Earth Sciences and Geography.

How Does Radiocarbon Dating Work? – Instant Egghead #28